1. Field of the Invention
The present invention relates to a thermal printer and a method of cleaning a thermal head thereof.
2. Description of the Prior Arts
A color thermal printer prints a full color image on a color thermal recording paper. The color thermal recording paper includes yellow, magenta, cyan thermosensitive coloring layers overlaid in sequence. Except for the cyan thermosensitive coloring layer, other thermosensitive coloring layers have a fixing property. While the recording paper is fed, a heating element array of a thermal head is pressed against the recording paper so that each heating element generates heat, and then three-color images are recorded in frame-sequential fashion by the heating. Ultraviolet rays having a peculiar wave-length range relative to each thermosensitive coloring layer are applied to the yellow and magenta thermosensitive coloring layers to fix the recorded image.
If the printing is continuously carried out, foreign matters are adhered or deposited to the heating element array, for example dust adhered to a printing surface of the recording paper, peeled matters peeled from a protective layer, which covers the printing surface of the recording paper, paper dust, and so on. If the printing is performed in a state the foreign matters are adhered to the thermal head, heat transfer is impeded so that the print image quality is degraded. If the thermal head is caused to preheat before printing, the adhered foreign matters are fixed to the heating element array by application of the heat, and therefore the contamination of the thermal head is deteriorated.
Accordingly, the color thermal printer should be regularly cleaned. In the prior art, a cleaning sheet is set in the printer instead of the color thermal recording paper, and then it is rubbed against the heating element array, so that the foreign matters adhered to the heating element array are eliminated. Japanese Patent Laid-Open Publication No. 10-100365 discloses the method of eliminating the foreign matters from the thermal head every printing. The ability of eliminating the foreign matters is subsidiary in comparison with the case in which the cleaning sheet is used. In this method, the foreign matters are wiped away from the heating element array by feeding the recording material in a state that the heating element array in an off-state is pressed against the recording material after printing.
However, as shown in FIG. 7, since the unheated color thermal recording paper 2 is hard, even if the color thermal recording paper 2 is pushed by a platen roller 4, a contact width W1 between the heating element 3 and the color thermal recording paper 2 is narrow. Thereby, the heating element 3 and the color thermal recording paper 2 are contacted with each other only in an upstream side part in the feeding direction of the recording paper. Therefore, it is not possible to eliminate the foreign matter 5 adhered to a downstream side part in the feeding direction of the recording paper.
There is also a known printer which is used with the rolled color thermal recording paper. When the power is turned off, a power turn-off operation is performed to rewind the unused recording paper to a roll. If paper jamming occurs when rewinding the recording paper, the foreign matters, which are adhered to the platen, are moved to the heating element array due to maintenance when the paper jamming has been occurred or when the recording paper and the heating element array have been scraped with each other in the paper jamming. If a reset operation is performed in order to fix an error occurred in the printer, an initializing operation for restoring an initial state of the printer is performed. In the initializing operation, since the heating element array and the platen are contacted with each other, the foreign matters adhered to the platen are moved to the heating element array.
Likewise, dust penetrating into the printer in exchanging or supplying the recording paper, paper dust, a printing residue and the like are also adhered to the heating element array. In Japanese Patent Laid-Open Publications No. 10-100365, since the heating element array is cleaned after printing, it is not possible to remove the foreign matters, which have been adhered to the heating element array after cleaning. Therefore, there arises a problem in that the foreign matters are fixed to the heating element array by preheating prior to printing so that the contamination is deteriorated.